Electrode for electron discharge devices



Nov. 20, 1934. E. A. GIARD I ELECTRODE FOR ELECTRON DiSCHARGE DEVICESFiled March 26, 1932 Patented Nov. 20, 1934' PATENT OFFICE ELECTRODE FORELECTRON DISCHARGE DEVICES Eugene A. Giard, Shorewood, Wis., assignor toI Cutler-Hammer, Inc., Milwaukee, Wis., a corporation ol. DelawareApplication March 26, 1932, Serial No.. 601,404

8 Claims.

This invention relates to an improved material for electrodes andespecially control electrodes or gridsof electron tubes.

In my application, Serial No. 557,221, filed on August 15, 1931, it waspointed out that control electrodes of electron tubes, especially whenthe cathode is coated with an emission increasing material, may producesecondary emission when they become heated from various causes duringoperation and that such secondary emission can be reduced by theemployment of certain metals and subjecting such metals to a superficialoxidizing process. Among the metals heretofore proposed is tantalum, buttantalum is very expensive and in the prior application I have proposedan electrode equipped with an oxidized tantalum surface. I have nowfound that similar and even more beneficial results can be obtained byalloyv ing nickel with a very small amount of beryllium and oxidizingthis alloy superficially.

An object of the invention is to provide an electrode which isinexpensive to manufacture and which yet has the desirablecharacteristics of electrodes which heretofore have been manufactured ofhigh grade and expensive material.

Another object of the invention is to provide an electrode of ruggedconstruction and of a relatively inexpensive material with a coatingwhich prevents secondary emission.

Another object is to provide an electrode having an oxidized berylliumsurface and requiring a minimum of beryllium metal.

The accompanying drawingshows one form of an electron tube with whichthe present invention may be employed, it being understood, however,that the invention is advantageous in connection with other types oftubes employing a control electrode.

In the drawing, 1 designates a glass or other container which in thepresent case may be filled with a highly attenuated gas or with mercuryvapor, 2 is a heated cathode and 3 an anode, while 4. is a controlelectrode consisting in the present case of an imperforate metal sheetwhich completely encloses the cathode except for openings at its'upperend opposite the anode. In the past such control electrodes were made ofpure tantalum and were subsequently superficial- 1y oxidized so as toreduce the secondary emission during operation.

According to the present invention, the grid is made of an alloy ofnickel and beryllium containing about 2% of beryllium. It should beunderstood, however, that the amount of beryllium may be higher or lessbut it has been found that a 2% admixture of beryllium is sufficient toobtain the satisfactory results aimed at. After the grid has been giventhe desired shape the surface is oxidized by heating it in air. Thisproduces on the surface a layer consisting of a mixture of the oxides ofnickel and beryllium. After the tube is completed, it is again heatedduring the exhausting process by means of a high frequency currentinduced in the conductlng'elements. This heating either reduces orvaporizes the nickel 05 oxide or does both and leaves a substantiallypure beryllium oxide film on the surface of the grid.

It is possible to produce the beryllium oxide layer on the surface ofthe grid by other methods such as the deposition'and subsequentoxidation of beryllium on a nickel base and I wish it to be understoodthat I do not'limit myself to the production of the beryllium oxidesurface by the method described heretofore,

A tube constructed in the aforedescribed manner and equipped with acoated. cathode was tested when new and showed a cathode emission ofapproximately .05 micro-amperes. After being in continuous operation forabout one month above the rated temperature of the filament and withanode current flowing the tube was tested. again and the cathode-gridcurrent was less than it was initially. A pure nickel grid would haveshown an appreciable increase of secondary emission after being operatedover such an extended 8 period. I

The conclusion to be drawn is therefore that the oxidized berylliumsurface of the grid combines with the compounds vaporized from thecathode and deposited on the grid to form thermionically inactivecompounds in a way similar to those formed on oxidized tantalumsurfaces.

While the invention has been described in connection with gaseouselectron tubes it may also be employed in high vacuum and other types oftubes having a control electrode subject to secondary emission, and withother electrodes capable of yielding undesirable secondary emissionunder the conditions obtaining in the tfibe.

What I claim as new and desire to secure by Letters Patent is:

1. An electrode for an electron discharge tube comprising a berylliumalloy having an oxidized beryllium surface. 3

2. An electrode for an. electron discharge device comprising a,beryllium alloy having a surface which is substantially composed ofberyllium oxide.

3. An ihtrode for an electron discharge tube comprising a berylliumalloy having a substantial 7. In combination with anelectron dischargedevice; a control electrode having a surface composed of a berylliumcompound.

8. The method of surfacingan electrode comprising a beryllium alloy,with a beryllium oxide coating which consists in subjecting theelectrode to an oxidizing treatment and reducing the re-,

suiting oxide mixture to remove an oxide but that of beryllium' EUGENEA. GIARD.

